Some earth moving machine, for example dozers, motor graders, and snow plows, have a front-mounted work tool such as a blade, bucket, or plow for pushing or carrying material. These work tools can be tilted about a horizontal axis generally perpendicular to the work tool by one or more tilt cylinders, and pitched about a horizontal axis parallel to the work tool by dual cylinders located to either side of the work tool. Tilting may be accomplished by extending and retracting a single cylinder or extending one paired cylinder while retracting the other paired cylinder. Pitching can be separately accomplished by extending or retracting both paired cylinders in the same direction at the same time. Existing hydraulic systems utilize different combinations of manual and/or pilot control valves to regulate the tilting and pitching operations.
An exemplary hydraulic system having tilt control is disclosed in U.S. Pat. No. 6,481,506 (the '506 patent) issued to Okada et al. on Nov. 19, 2002. Specifically, the '506 patent discloses a hydraulic system having a left tilt cylinder and a right tilt cylinder connected between straight side frames of a machine and outer edges of a blade. The hydraulic system also includes a left cylinder actuation switching valve (LCASV), a right cylinder actuation switching valve (RCASV), a left post-pressure compensating valve associated with the LCASV, a right post-pressure compensating valve associated with the RCASV, and a pilot switching valve. Each of the LCASV and RCASV are pilot-operated valves configured to move between first positions at which pressurized fluid from a pump is directed into head-ends of the associated tilt cylinders, and second positions at which pressurized fluid is directed into rod-ends of the associated tilt cylinders. The pilot switching valve is a solenoid-operated valve movable between a first position at which the head-ends of both the LCASV and RCASV receive the same pilot pressure, and a second position at which the head-end of the LCASV and the rod-end of the RCASV receive the same pilot pressure. In this configuration, the hydraulic system may be capable of separately implementing a pitch operation utilizing both LCASV and RCASV, a single-tilt operation using only LCASV, or a dual-tilt operation using LCASV and RCASV.
Although the system of the '506 patent may be capable of separately implementing both tilt and pitch operations, it may still be limited. That is, the system of the '506 patent may not be capable of simultaneously tilting and pitching, or of accomplishing single-tilt operations using only the RCASV. These limitations may reduce functionality of the associated machine.
The hydraulic system of the present disclosure addresses one or more of the needs set forth above and/or other problems of the prior art.